1. Field of the Invention
This invention relates to curing agents for epoxy/anhydride resins. There are a wide variety of two component compositions available for finishing substrates. Generally, the mixing of the components occurs before application, and addition of a curing agent results in a product with a relatively short (several hour) shelf life. The present invention which teaches the use of amine-borane adducts as curing agents improves the usable time in which the composition can be applied to a substrate at the application stage and offers short cure times and harder surfaces.
Also provided is an improved process for the preparation of tertiary amine borane adduct curing agents.
Resins containing the curing agents of the current invention are used in coatings, laminates, moldings, castings and adhesives.
2. Prior Art
Commonly assigned patent application Ser. No. 07/051,867 U.S. Pat. No. 4,816,500 discloses and claims a coating composition containing 20-80% by weight of reactive binder components and 80-20% by weight of an organic carrier; the binder contains about (a) 50-95% by weight, based on the weight of the binder, of an acrylic polymer having at least two reactive anhydride groups which consist of polymerized monomers of an ethylenically unsaturated anhydride and polymerized monomers selected from the group consisting or alkyl methacrylate, alkyl acrylate and any mixtures thereof, wherein the alkyl groups have 1-8 carbon atoms and the polymer has a weight average molecular weight of about 2,000-50,000; (b) 5-50% by weight, based on the weight of the binder, of a glycidyl component having at least two reactive glycidyl groups; and the composition contains about 0.1-5% by weight, based on the weight of the binder, of a catalyst (curing agent); and wherein the primary reaction on curing of the composition occurs between the anhydride groups of the acrylic polymer and the glycidyl groups of the glycidyl component and wherein the composition upon curing forms a hard glossy and tack free finish.
The useable time in which the composition can be applied by conventional means such as that in Ser. No. 07/051,867 is about 1 to 6 hours depending on the surrounding temperature conditions.
U.S. Pat. No. 3,013,016 describes the synthesis of trialkylamine borane adducts using sodium or potassium borohydride, an acid such as carbon dioxide, the parent amine and a water immiscible solvent. Water is also present during the reaction.
Czech Patent 242,064 also describes a process for the preparation of tertiary amine borane adducts in which a metal borohydride, carbon dioxide, a tertiary amine and a solvent are mixed (the borohydride is present as a suspension), allowed to react, and then the reaction mixture is washed with water, and the solvent evaporated. Absence of water during the reaction step eliminates the potential side reaction of the borohydride with water.